Peroxynitrite formation and decreased catalase activity in autoimmune MRL-lpr/lpr mice

Background: (MRL)-lpr/lpr mice spontaneously develop autoimmune disease cha racterized by arthritis and glumerulonephritis. Nitric oxide is postulated to play a role in the disease pathogenesis, as mice treated with the nitric oxide synthase inhibitor N-G-monomethyl-L-arginine (NMMA) show markedly re duced manifestations of the disease. The purpose of this study was to exami ne the role of peroxynitrite in disease development in MRL-lpr/lpr mice. Materials and Methods: We examined kidney extracts from control and MRL-lpr /lpr mice for nitrotyrosine by immunoblot with a rabbit polyclonal anti-nit rotyrosine antibody. Catalase activity was determined spectrophotometricall y or by activity staining of native polyacrylamide gels. In some experiment s, we studied the ability of peroxynitrite and other agents to modify purif ied catalase in vitro. Results: Kidney extracts from diseased mice had elevated levels of nitrotyr osine, and decreased levels of catalase activity and protein, relative to c ontrol mice. MRL-lpr-lpr mice treated with NMMA in vivo had decreased level s of nitrotyrosine, and demonstrated a partial restoration of both catalase activity and protein levels. Treatment of catalase in vitro with peroxynit rite or tetranitromethane at pH 8.0 resulted in protein nitration and a dec rease in catalase activity. 1,3-morpholinosydnonimine (SIN-1), a peroxynitr ite generator, also decreased the activity of catalase. Conclusions: These observations suggest that peroxynitrite formation, with an associated decrease in catalase activity and general decrease in antioxi dant enzyme activity, may result in increased levels of hydrogen peroxide a nd other oxidants that can contribute to the pathogenesis of disease in MRL -lpr/lpr mice.